1 / 52

URINARY SYSTEM

URINARY SYSTEM. Functions. Excretion removal of organic wastes from body fluids Creatinine- by-product of muscle metabolism Nitrogenous wastes- urea from protein break down Elimination discharge of wastes from body micturition Homeostasis help regulate

lyn
Download Presentation

URINARY SYSTEM

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. URINARY SYSTEM

  2. Functions • Excretion • removal of organic wastes from body fluids • Creatinine-by-product ofmuscle metabolism • Nitrogenous wastes-urea from protein break down • Elimination • discharge of wastes from body • micturition • Homeostasis • help regulate • blood volume-has effects on blood pressure • osmolarity-by integrating kidney function with behavioral drives such as thirst • ion balance-Na, K & Cl • pH • Detoxification • excrete foreign substances found in blood • drugs and toxins

  3. Urinary System • Kidneys • bean-shaped organs • either side of backbone • retroperitonealarea • between dorsal body wall & parietal peritoneum • Hilum • area for entrance of blood vessels, nerves, etc. • excretory functions • produce urine • Ureters • hollow tube • peristalsis moves urine to bladder • Bladder • urine storage • capable of expanding • transitional epithelium • Urethra • carries urine to outside

  4. Kidney Structure • Renal Cortex • outer • lightcolored • Renal Medulla • deeper • made of 6-18 cone shaped tissue masses-renal pyramids • base of each faces cortex • striped appearance • collecting tubules • Renal columns • inward extensions of cortical tissue • separates pyramids • tip of each pyramid-renal papilla • projects into renal sinus • ducts in renal papilla discharge urine into minor calyx • 8-18 minor calycesmergemajor calyx • 2-3 majorcalicesrenal pelvisureterbladder

  5. Blood Supply • served by renal artery • enters hilus segmental arteries  interlobar a. arcuatea. interlobular aretery  feeds renal lobes • branch of interlobular a. afferent arteriole glomerulus • departs by efferent arterioledrains into peritubular capillaries surrounding nephron interlobular veinarcuate v interlobar v renal vein

  6. Nephron • basic structural & functional unit • comprise bulk of kidneys • 1 X 106 per kidney • urine production begins • 85%-in cortex • cortical nephrons • others begin in cortex & dip intomedulla • juxtamedullarynephrons • consists of renal tubule + renal corpuscle • renal tubule • long tube beginning at renalcorpuscle • renal corpuscle • consists of capillary network-glomerulus & a two layered Bowman's or glomerular capsule

  7. Renal Tubules • proximal convoluted tubule • leaves glomerular capsule • remains in cortex • loop of henle • hairpin loop • descending & ascending limbs • extends into medulla • distal convoluted tubule • forms end of tubule • leads into collecting duct

  8. Renal Corpuscle • things leaving plasma pass through renal corpuscle • Bowman’s capsule + glomerulus • Bowman’s capsule • outer, parietal layer • made of simple squamous epithelieum • inner visceral layer • madeof podocytes • Podocytes wrap around capillaries of glomerulus • forms filtration membrane • comprised of glomerular capillaryvisceral endothelium, basal lamina&simple squamous parietal epithelium of Bowman’s capsule • capsular space separates parietal & visceral epithelia • glomerular capillaries are fenestrated • pores-large allowing most blood components to filter out of plasma but small enough so RBCs cannot escape. • podocytes terminate in foot like processes called pedicels that intertwine forming openings-filtration slits

  9. Juxtaglomerular Apparatus-JGA • group of epithelial cells of DCT near renal corpuscle • taller than cells located elsewhere along duct • nuclei are clustered together forming macula densa • lies adjacent to juxtaglomerularcells (JC) • Macula densa + JC cells = JGA • secretes renin & erythropoietin

  10. Renal Physiology • goal of kidneys is to maintain homeostasis • does so by regulating blood volume & blood composition • involves excretion of solutes • Urea • produced by amino acid breakdown • Creatinine • generated by skeletal muscle breakdown of creatinine PO4 • uric acid • formed by recycling nitrogenous wastes from RNA • solutes are dissolved in blood • only eliminated dissolved in urine • therefore to remove them kidney must also remove water • kidneys concentrate urine to prevent excess fluid loss

  11. Urine Formation • result of 3 processes • Filtration • Reabsorption • Secretion

  12. Filtration • blood pressure forces water & dissolved solutes out of capillaries into capsular space • function of glomerulus • only occurs at renal corpuscle • solutes removed from plasma by size as fluid moves from blood into lumen of nephron-passive • bad & good things are filtered out • creates filtrate • liquidalmost identical to plasma in composition-glomerular filtrate • similar to plasma but without proteins • two are nearly isoosmotic • 180 L of plasma move into nephrons each day • destined for removal

  13. Tubular Reabsorption • removal of waste & solute from filtrate • from lumen of nephron into peritubular capillaries & back into blood • job of renal tubules • primary function of proximal tubules • material not reabsorbed passes from proximal tubule into Loop of Henle • primary site for creation of dilute fluids • filtrate passes through loop • more solute is reabsorbed than water • producing hypoosmostic fluid • by time filtrate leaves loopaverage osmolarity is 100mOsm • volume has been reduced to 18L • from loop of Henle filtrate passes into distal tubule &collecting ducts • fine regulation of Na & water balance • hormonally controlled

  14. Tubular Secretion • movement of fluid from blood into tubular fluid • selective • takes place along length of renal tubules • backs up filtration • filtration does not force all dissolved materials out of plasma

  15. Glomerular Filtration • passive, non-selective • fluids & solutes are forced through filtration membrane by hydrostatic pressure • filtration membraneis simple • mechanical filter • requires nometabolic energy • water & small molecules are filtered out by size • determined by fenestrations & slits of filtration membrane

  16. Glomerular Filtration • primary pressures involved • GBHP-glomerular bloodhydrostaticpressure • result ofblood pressure in glomerular capillaries • higher here than elsewhere • about 55 mm Hg • because afferent arteriole is much larger than efferent arteriole • change in diameter creates resistance & therefore higher pressure is needed to force blood into efferent arteriole • pressure pushes water & solutes out of plasma into filtrate • GBHP-opposed by capsular hydrostatic pressure-CHP • about 15mm Hg • capsular hydrostatic pressure tends to push water & solutes out of filtrate into plasma

  17. Glomerular Filtration • BCOP-blood colloid osmotic pressure • pressure due to proteins in blood • 30mm Hg • NFP-net filtration pressure equals • GBHP – CHP – BCOP • 55 mm Hg -15mm Hg -30mm Hg = 10 mm Hg • favors filtration

  18. Glomerular Filtration Rate-GFR • amount of filtrate formed/minute • normal-125ml/min for males & 105ml/min for females • homeostasis of body fluids requires that kidneys maintain relatively constant GFR • if too high substances pass so quickly that some are not reabsorbed & are lost in urine • if too low, nearly all filtrate may be reabsorbed & certain wastes may not be eliminated & ph control may be jeopardized

  19. Glomerular Filtration Rate-GFR • GFR is related to pressures that determine filtration pressure • any change in NFP will affect GFR • NFP is determined by renal blood flow & blood pressure • changes in either will affect GFR • severe blood loss reduces MAP (mean arterial pressure) & decreases glomerular blood hydrostatic pressure • filtration ceases if GBHP drops to 45mm Hg because opposing pressures add up to 45mm Hg • when systemic blood pressure rises above normal NFP, GFR increases very little • GFR is nearly constant when blood pressure is 80 – 180mm HG

  20. Controlling GFR • regulatory mechanisms ensure GFR is kept within normal limits • mechanisms that regulate GFR • adjust blood pressure into & out of the glomerulus • alter glomerular capillary surface area available for filtration • GFR increases when blood flow into glomerulus increases • 3 mechanism control GFR • renal autoregulation • nervous regulation • hormonal mechanisms

  21. Renal Autoregulation • ability of nephrons to adjust own blood flow & GFR • two mechanisms • myogenic mechanisms • tubuloglomerular feedback

  22. Myogenic Mechanisms • works by changing diameter of afferent arteriole • based on tendency of smooth muscle to contract when stretched • increase in blood pressure increases GFR because renal blood flow increases • blood pressure increasessmooth muscles in afferent arteriole’s wall stretchesmuscle cells contract narrows lumen of arteriole (vasoconstriction)increases resistance to flow blood flow to glomerulus decreasesreduces GFR to previous level • blood pressure decreasessmooth muscle cells stretched lessafferent arteriole dilatesrenal blood flow increasesGRF increases • normalizes blood flow & GFR within seconds

  23. Tubuloglomerular Feedback • when GFR is above normal due to elevated blood pressurefluid flows more rapidly along tubules • as a result PCT & loops of Henle have less time to absorb Na, Cl & water • macula densa cells detect this inhibit release of nitrous oxide (NO) from cells in JGA • NO causes vasodilation • when level is low afferent arterioles constrictblood flow into glomerular capillaries is less decreases GRF • when blood pressure decreases , GFR is lower than normal opposite happens method is slower than myogenic method

  24. Neural Regulation of GFR • autoregulation cannot compensate for extreme blood pressure changes • sympathetic nerve fibers supply efferent & afferent arterioles • blood pressure risesrelease norepinephrinebinds to alpha one receptors in afferent arteriolesvasoconstriction inhibits filtrate formation decreases GFR • at rest sympathetic innervations is moderately lowafferent & efferent arterioles are dilatedrenal autoregulation controls GFR • moderate sympathetic stimulationafferent & efferent arterioles contract to same degree blood flow into & out of glomerulus is restricted to same extentdecreases GFR only slightly • greater stimulation of sympathetic nerves (exercise, hemmorage)afferent arteriole constrictsblood flow & GFR decreased • lowering renal blood flow has two consequences: reduces urine output which helps to conserve blood volume • permits greater flow of blood to other tissues

  25. Hormonal Control • 2 hormones contribute to GRF regulation • Angiotensin II-reduces GFR • Vasoconstrictor • causes constriction of both afferent & efferent arterioles reduces renal blood flow & decreases GFR • ANP (atrial natriuretic peptide) made in atria of heart • increases GFR • blood volume increasesatria stretchANP secretedrelaxes glomerular mesangial cellsincreases surface area available for filtrationGFR increased as surface area increases

  26. Renal Tubules • Proximal convolutedtubule • absorbs organic nutrients, ions & water • Loop of Henle • descending limb • ascending limb • peritubular capillaries connect limbs to vasa recta • long straight capillaries in medulla running parallel to loop of Henle • distal convoluted tubule (DCT) • initial part passes between afferent & efferent arterioles • secrete solutes into filtrate • reabsorbs Na, Ca &water • opens into collecting ducts • receives filtrate from many nephronspapillary ductminor calyx

  27. Reabsorpton • recovers useful materials that enter filtrate • organic nutrients • facilitated transport & cotransport • 90% of glucose, amino acids & other organic nutrients reabsorbed by PCT • PCT actively transports Na, K, Mg, HCO3, PO4 & SO4 • 90% of bicarbonate is reabsorbed by PCT • 65% water is reabsorbed by osmosis at PCT • passively reabsorbs urea, Cl & lipid soluble materials • ascending limb reabsorbs Na, K & Cl • DCT reabsorbs Na, Cl, HCO3, water • Collecting duct reabsorbs water and urea

  28. Reabsorpton Methods • Diffusion • Osmosis • Carrier mediated transport • facilitated diffusion • uses carrier protein transports without spending energy • activetransport • uses ATP • includes pumps & carrier proteins • cotransport • 2 substrates cross membrane bound to one carrier protein • counter (anti) transport • 2 transported substances move in opposite directions

  29. Transport Maximum • transport proteins are limited • there is a limit to amount of solute that can be reabsorbed • all transport proteins are full • saturation point • transporters are saturated some solute will appear in urine • maximum rate of transport is reached • transport maximum Tm • Tm determines renal threshold • plasma concentration at which specific compound appears in urine • renal thresholds vary with substance • glucose-180mg/dL • normal plasma glucose concentrations- all glucose entering nephron is reabsorbed before reaches end of proximal tubule • tubule epithelium has enough carriers to capture glucose as flows past • glucose concentrations too highcarriers saturatedglucose in urine

  30. Tubular Secretion • transports materials from blood into glomerular filtrate • in PCT & nephron loop secretion serves to remove waste-urea, uric acid, bile acids, ammonia, catecholamines, prostaglandins & creatine • tubule secretion of hydrogen & bicarbonate ions help regulate pH levels

  31. Nephron Loop & Urine Formation • limbs have different permeability • descending limb • permeable to water • impermeable to solutes • ascending limb • impermeable to water & solutes • has active transport mechanisms to pump Na, Cl & K from tubular fluid into extracellular fluid

  32. Nephron Loop & Urine Formation-Countercurrent Mechanisms • countercurrent multiplication • countercurrent exchange • reabsorb water & solutes before tubular fluid reaches DCT • establish concentration gradient that allows passive reabsorption of water from tubular fluid into collecting system

  33. Counter Current Multiplication • descending & ascending limbs of Henle are close together • separated by peritubular fluid • exchange occurring between -counter current flow • Countercurrent • flow between fluids moving in opposite directions • Multiplication • effectof exchange increases as fluid movement continues • Osmolarity increased from cortex to deeper medulla

  34. Consequences of Permeability Differences • descending limb • permeable to water • impermeable to solutes • water passes by osmosis from tubule into extracellular fluid leaving salt behind • tubule contents continue to increase in osmolarity reaching about 1200 mOsm/L by time fluid reaches bend at end of loop • keeps osmolarity of medulla high • ascending limb • impermeable to water & solutes • has active transport mechanisms to pump Na, Cl & K from tubular fluid into extracellular fluid • water remains in tubule making tubular fluid more and more dilute as nears cortex • about 100 mOsm/L by time reaches top of loop

  35. Counter Current MultiplicationReview • Na & Cl pumped out of ascending limb into ECF • elevates osmotic concentration in extracellular fluid (ECF) around descending limb resulting in osmotic flow of water out of descending limb ECF • descending limb is permeable to water but not to solutes • removal of water increases solute concentration in descending limb • fluid becomes hypertonic • arrival of highly concentrated solution in ascending limb (osmolarity of filtrate peaks at elbow of loop at 1200mOsm) accelerates transport of Na & Cl into ECF of medulla • osmolarity of medullaincreases along descending limb • no osmosis can occur at ascending limb because is not permeable to water • as Na & Cl are removed solute concentration in tubular fluid decreases becoming hypotonic • positive feedback arrangement • key to making concentrated urine is high osmolarity of medulla • without this there would be no concentration gradient & as result no osmotic movement of water. • loss of Na & Cl from lumen causes osmolarity of tubule fluid to decrease from 1200 to 100 mOSM at cortex • net result • high solute concentration generated & maintained in medulla while tubule fluid becomes hypotonic

  36. Countercurrent Exchange-Vasa Recta • blood vessels surrounding nephron-vasa recta • water & solutes which move into surrounding tissue are removed by vasa recta • freely permeable to water & salt • return water to blood • maintain high osmolarity of medulla

  37. Hormonal Control of Reabsorption withouthormones, distal tubules & collecting ducts are relatively impermeable to water • 5 hormones affect extent of Na, Cl, Ca & water reabsorption & K secretion by renal tubules • angiotensin II, aldosterone, ADH, ANP & PTH

  38. Angiotensin II Control of Reabsorption • blood volume or blood pressure decrease walls of afferent arterioles stretched lessJG cellsrenin • converts angiotensinogenangiotensin I • angiotensin converting enzyme, ACE, in lungs, proximal tubules & other tissues, converts angiotensin I to angiotensin II • angiotensin IIvasoconstricts afferent arteriolesincreases blood pressure increases GFR • stimulates NaCl & water reabsorption at proximal convoluted tubule • stimulates adrenal cortex to secrete aldosterone • promotes sodium & water retention by distal convoluted tubule & collecting duct • Angiotension II further stimulates secrection of ADH by pituitary water reaborption increases & stimulates thirst to encourage behavioral changes in water consumption • all together these raise blood pressure by reducing water loss, encouraging water intake & constricting blood vessels

  39. Aldosterone • reninadrenal cortex aldosterone  water & Na retention increases blood volume & blood pressure • aldosterone stimulates principle cells in collecting ducts to absorb Na and Cl & to secrete more K ions

  40. ADH • ADH or vasopressin released from posterior pituitary regulates facultative reabsorption of water by increasing water permeability of principle cells in late part of DCT & collecting ducts • Na & water reabsorption are separately regulated in distal nephron • Facultative-reabsorption of water not coupled to other solutes • Obligatory-reabsorption of water that is coupled to other solutes-where sodium goes water follows

  41. ADH • within principle cells are tiny vesicles containing many copies of water channel proteins-Aquaporin-2 • ADH stimulates insertion of these into apical membrane of cells in DCT & collecting ductsincreases water permeability • controlled by negative feedback mechanism • osmolarity or osmotic pressure of plasma is increased (ie. when water concentration is low) osmoreceptors in hypothalamus detect changesends impulses to posterior pituitaryADHprinciple cells more permeable to waterwater reabsorption increasesplasma osmolarity returns to normalosmoreceptors noticestop ADH release

  42. ANP • made by atria of heart • inhibits reabsorption of Na & water in PCT and collecting duct • also suppresses secretion of ADH & aldosterone • these increase excretion of Na in urine • increases urine output which decreases blood volume & blood pressure

  43. Parathyroid Hormone • released from parathyroid gland in response to low levels of blood calcium • increases Ca reabsorption by early DCT

  44. Evaluation of Kidney Function • several ways to determine how effectively kidneys are functioning • most used & easiest of these test is urinalysis • urine is evaluated for volume, physical & chemical properties • renal clearance • way to access functions & to access renal function indirectly • volume of blood cleaned or cleared of a substance per unit time (ml/min) • assesses renal function by using urine &blood values • Renal Clearance = S = U X V/P U=concentration of substance in urine, P=concentration of substance in plasma and V= urine flow in ml/minute

  45. Renal Clearance • Renal clearance (C) = UV/P • U = urea concentration in urine • V = rate of urine output • P = urea concentration in plasma • U = 6.0 mg/ml, V = 2ml/min and P = 0.2 mg/ml then C = 60ml/min • means 60ml of blood is completely cleared of urea each minute • estimates GFR • cannot be exactly determined by urea excretion • some urea is secreted into renal tubule and not filtered by glomerulus and some urea that is filtered by glomerulus is not reabsorbed

  46. Renal Clearance • depends on 3 basic processes: filtration, secretion & reabsorption • for a substance that is filter but not reabsorbed or secreted clearance = GFR • all the molecules that pass filtration membrane appear in urine • GFR can be obtained with inulin • polysaccharide from dahlia plant • not normally found in body • neither reabsorbed or secreted • rate at which it appears in urine can be used to calculate GFR • all inulin will befiltered & end up in urine • for inulin GFR = Renal Clearance = 125ml/min

  47. Creatinine Clearance Test • can be used to estimate GFR • compares blood & urine creatinine concentrations • creatinine-breakdown product of phosphocreatine • energy storage compound in muscle • produced & removed at constant rate from blood • filtered & not reabsorbed in significant amounts (15%) • only 2 ways for substance to be in urine • filtered at glomerulus or secretedfrom peritubular capillaries into tubules • GFR = amount of substance eliminated divided by amount of substance in plasma • Kidneys eliminate 84mg of creatinine/hour & plasma creatinine = 1.4mg/dL • 84/1.4 = 60dL/hr = 100ml/min • because nearly all creatinine appears in urinechange in rate of creatinine excretion may reflect renal disorder

  48. Excretion • Filtration • occurs as blood flows through glomerulus • removes materials from blood • Reabsorption • materials & fluids are taken back into the blood • Secretion • along nephron tubular system • substances not cleared by filtration are placed into filtrate • resulting fluid called urine bears little resemblance to filtrate made at Bowman’s capsule • glucose, amino acids, useful metabolites have been reabsorbed • organic wastes have become more concentrated

  49. Ureters • from collecting ducts, urine enters renal pelvisureter • lined with transitional epithelium

More Related